Often, such questions are followed up with unsolicited advice based on folk wisdom or anecdotes.

Myths and folklore about pregnancy, labor and delivery abound. They persist in part because of the difficulties in conducting properly controlled scientific studies on pregnant and breast-feeding women and their newborns. In particular, researchers are loath to test medicines on pregnant women in the wake of the thalidomide disaster.

Much of the advice women get is relatively harmless — abstain from alcohol, caffeine and sex — but because of the research gap, it often isn't backed up by rigorous scientific study. Putting women on bed rest to prevent miscarriages is a prime example: There's very little evidence of effectiveness, yet it persists in medical practice for lack of better, research-based treatment options. "Pregnancy and birth are two of the greatest unknowns in science," says Tonia Moore-Davis, director of the nurse-midwife practice at Vanderbilt University School of Nursing in Nashville.

Such recommendations can seem like benign ways of ensuring a healthy pregnancy and baby, but the pressures on women pile up: Eat only the best foods (or your baby won't like broccoli later), gain weight in a very narrow range (or your child will be diabetic and obese); breast-feed exclusively for six months (even if you have to go back to work in six weeks).

In the last year, however, several studies or reviews of studies have looked carefully at popular pregnancy recommendations, and what they've found turns some of the folk wisdom on its head. Here's a look at what scientific evidence can really tell us — or not — about five topics in pregnancy, labor and delivery. Knowing what the science says gives women the chance to make their own informed decisions instead of relying on Internet rumors, kaffeeklatsch gossip and well-meaning, but sometimes uninformed, advice.

No good options for morning sickness

Though it's not a life-threatening condition, nausea associated with pregnancy is exhausting and miserable and can cause major losses in productivity. Unfortunately, research into effective treatments is lacking.

"It's seen as a 'normal' sign of pregnancy. But most women do suffer the effects of it, and the psychological effect can really get to people," says Anne Matthews, a midwife and lecturer of nursing at Dublin City University in Ireland. She's noticed more women turning to therapies such as acupressure, ginger and vitamin B6. "But there's a need for evidence. We don't really know if these are safe or effective."

Curious, she and a team of researchers reviewed the scientific literature to see which morning-sickness treatments had been tested in randomized, controlled trials. They found only 27 studies since 1959 that met the criteria. Treatments included acupuncture, acupressure, ginger, vitamin B6 and anti-nausea drugs such as hydroxyzine, thiethylperazine and doxylamine combined with B6. The review, published in September by the Cochrane Library, found that none of the remedies had enough scientific evidence behind them to be deemed effective.

"We were disappointed," Matthews says. "I'd prefer to have a clearer message. But there just isn't enough strong, reliable evidence to say whether things don't work or do work."

Her regretful recommendation to nauseated women: "Strictly speaking, I would have to say, nothing."

Sex during pregnancy is safe for most

It is one of the most common questions obstetricians get from patients: When is it OK to have sex during pregnancy?

"Many patients and their partners are afraid about having sex," says Dr. Claire Jones, a resident physician in obstetrics and gynecology at Mt. Sinai Hospital in Toronto. "People turn to the Internet for this kind of information, and the things you can read there are ridiculous."

Yet from a review she co-authored (published in January in the Canadian Medical Assn. Journal), the findings were clear: "For healthy women who have an otherwise healthy pregnancy, there is no reason not to have sex and enjoy it."

That's not the case for all women, she cautions. Those with a condition called placenta previa, in which the placenta covers the opening of the cervix, should abstain because there is a risk that anything penetrating the cervix could cause bleeding from the placenta.

Women at risk for preterm labor are usually told to abstain as well. Most of the studies that have looked at this issue concluded that the chance of sex causing preterm labor was only higher in women who also had a lower genital tract infection. But because such infections can go unnoticed during pregnancy, doctors err on the side of caution and recommend avoiding sex if you are at risk for preterm labor.

Some couples think that sexual intercourse near the end of pregnancy might induce labor. There is good theory behind this popular belief: The hormone released by orgasm, oxytocin, is the same one doctors use to induce labor. In addition, semen contains molecules called prostaglandins, which are also used by doctors inducing labor to help "ripen" the cervix. The few studies examining this question have been inconclusive, Jones says.

"Every doctor has anecdotes of patients who have tried it and went into labor the next day," Jones says. For uncomplicated pregnancies, she says it's safe for couples wanting to kick-start labor to try.

Light drinking of alcohol may be OK

It's well known that moderate, heavy or binge alcohol consumption during pregnancy can lead to fetal alcohol spectrum disorders, which can include facial deformities, low birth weight, delayed development, mental retardation and heart and other birth defects. But until recently, no one had taken a close look at the consequences of much lower levels of alcohol consumption during pregnancy.

In the U.S., complete abstinence from alcohol during pregnancy is promoted by the surgeon general, the Centers for Disease Control and Prevention and other public health agencies. That's because no one has ever conducted (nor likely will ever conduct) a study to determine if there is a safe level of alcohol consumption during pregnancy. Scientists were, however, able to get at the issue by taking advantage of more lenient attitudes that exist in Britain, where the Department of Health recommends that if pregnant women choose to drink, they should have no more than two drinks once or twice per week to protect a baby's health.

Yvonne Kelly, an epidemiologist at University of Essex in Colchester, England, and colleagues analyzed data from more than 18,500 families with children born between September 2000 and July 2002. "We weren't setting out to say, 'Drink during pregnancy; it's good for you.' Rather, we were asking, 'Are these children really not at any increased risk [for problems] from light drinking?' " Kelly says.

The answer, she says, was very conclusively no — even after the team adjusted the stats as much as they could to rule out the influence of factors such as socioeconomic status, mother's health and age and parenting styles. Children born to mothers who drank an average of one to two drinks per week during pregnancy (or one to two drinks on a special occasion) had kids who performed just as well in cognitive and behavioral tests at age 3 and 5 as those born to women who usually drank alcohol but abstained during pregnancy.

"Children born to light drinkers don't appear to be at any increased risk for difficulties compared to women who chose not to drink in pregnancy," says Kelly of the finding, published in October in the Journal of Epidemiology and Community Health. But, she adds, "never, ever get drunk during pregnancy — it's bad for you and the child you are carrying."

Trying labor after a previous caesarean

Last year, the American College of Obstetrics and Gynecology (ACOG) revised its guidelines to doctors on vaginal birth after caesarean, or VBAC.

In the past, obstetricians had become increasingly concerned that women who had a scar across their uterus from a prior caesarean delivery and were at an increased risk of uterine rupture might suffer complications that could threaten the life of mom and baby. That perception fueled policies at hospitals, mainly dictated by liability insurance carriers that were unwilling to accept the extremely low but catastrophic risk of maternal and newborn death due to uterine rupture.

However, in 2010 the National Institutes of Health compiled the evidence from major VBAC studies, which included more than 20,000 women. It clearly showed how low the risks actually were, even for women who had had two previous caesarean deliveries.

For women with a normal pregnancy who had one previous caesarean, the risk of uterine rupture is less than 1%, the studies showed. For women with two previous caesareans, the risk is slightly higher but is still less than 2%.

The risk of maternal death (about .02%) was not increased at all compared with women who elected to have a repeat caesarean.

In its updated guidelines, changed to reflect the new data, ACOG concluded that a woman should be allowed to try for a VBAC provided she has none of the risk factors that can hinder vaginal birth and that the hospital has the capability to perform an emergency caesarean if needed. This usually means having an anesthesiologist on duty 24 hours. The new guidelines also allow a woman with two prior caesareans and a woman carrying twins to be candidates for VBACs.

"No one should be coerced into an operation they don't want," says Dr. William Grobman, maternal and fetal medicine specialist at Northwestern University in Chicago, who co-wrote the guidelines.

But, he adds, women and their providers should have early discussions to find a hospital that can safely accommodate trying for a VBAC.

On average, about 70% of women who try for a VBAC are successful, but for any individual woman and pregnancy, the chances may be much higher or lower depending on factors such as the baby's predicted weight and position at time of labor, and a mother's previous history of failed labors.

Grobman notes that, from a public health perspective too, women who fit the criteria should be encouraged to try for a VBAC — a successful vaginal birth is better for a mom's health and her future deliveries. But, he adds, it remains to be seen whether hospitals will change their policies.

Epidurals don't hinder breast-feeding

Around 70% of women in the U.S. receive epidural analgesia, an infusion of pain-blocking medicine directly to the spinal cord, during labor and delivery. A heavy dose of misinformation swirls around this common practice, handed down among women and on Internet forums. In part, this is due to the culture of childbirth education in the U.S., which largely favors natural or unmedicated birth as the best option for mother, baby and breast-feeding success.

Many women are wrongly advised that getting an epidural will slow down and prolong labor, leading to an increased chance of a forceps- or vacuum-assisted delivery or a caesarean. These and the epidural medicine itself, they are told, will make it harder to successfully establish breast-feeding in the hours and days after delivery because the newborn will be groggy, sluggish or sleepy from the medicines or experience of a "medicalized" birth.

Almost all of these ideas about epidurals have been debunked by research in the last decade (see related article), but the beliefs persist. That sets up many women to forego, or feel guilty about, what is arguably the most effective and safest form of pain relief for labor.

In 2006, an Australian study grabbed headlines when it seemed to confirm that the fentanyl medicine used in epidurals caused breast-feeding problems in newborns. But the study was extremely flawed, say researchers, in part because every woman who received an epidural also got a shot of pethidine (Demerol), a long-acting narcotic. Such narcotics are well-known to make babies groggy after delivery, so the breast-feeding troubles could easily have been caused by the pethidine alone.

Nonetheless, in the minds of natural childbirth advocates and the breast-feeding support community, fentanyl was the culprit.

There are medical reasons to suggest that probably isn't so. Although fentanyl, just like pethidine, is an opioid narcotic, the dose that goes into the spinal column during an epidural is small, and the amounts that get into the mother's bloodstream, across the placenta and into baby's bloodstream are tiny. What's more, fentanyl is a short-acting narcotic, meaning its effects are cleared in a matter of minutes to hours after the epidural catheter delivering the medicine is removed.

Dr. Matthew Wilson and other members of an epidural study group based in Britain realized they had the data to better test whether fentanyl was the bad guy.

In a study published last year in the journal Anaesthesia, they directly compared more than 1,000 women who had been randomly chosen to receive different types of epidurals — ones with and without fentanyl — and women who had no epidural at all. A day after delivery, the women were asked if they had established breast-feeding. One year later, they were asked how long they had breast-fed.

"There was really no difference between any of the groups" in terms of breast-feeding success, says Wilson, an obstetric anesthesiologist at Royal Hallamshire Hospital in Sheffield, England. "There was no evidence that fentanyl in an epidural has an effect on breast-feeding nor that having an epidural per se affects breast-feeding.

A woman considering an epidural "can be reassured that she's not reducing her chance of successful breast-feeding," he concludes.

Lactation experts remain unconvinced. "Different interventions at birth have a huge effect on breast-feeding down the road, because those first couple of weeks [are when] milk production is established and set," says Teresa Pitman, former executive director of La Leche League Canada, a breast-feeding support network, and co-author of "The Womanly Art of Breastfeeding."

Breast-feeding, she says, is the most complex behavior newborns must master: locating the nipple, latching on, sucking with the tongue placed properly and coordinating breathing with swallowing. Even a tiny amount of medicine might disrupt it, she argues. Higher rates of assisted deliveries could cause headaches in babies, overly swollen breasts from the intravenous fluids given along with epidurals, and post-epidural fevers that cause moms and babies to be separated.

Wilson and other anesthesiologists contend these ideas are based on speculation and not rigorous research. Dr. William Camann, head of obstetric anesthesiology at Brigham and Women's Hospital in Boston and co-author of "Easy Labor," calls the idea that epidural medications could affect a baby weeks later "completely ridiculous."

"If epidurals were dangerous or had downsides, three-fourths of women would not be getting them. The babies come out screaming, crying, and vigorous," he says.

Anesthesiologists and natural childbirth advocates do agree on some points, however:

Narcotic injections, delivered intravenously or into muscle, are riskier for a baby's health and successful breast-feeding than epidurals. "Narcotics are not good for baby and breast-feeding; they affect baby's initial alertness and ability to breast-feed," Camann says.

Adds Pitman: "With good help, most moms and babies can overcome any difficulties with breast-feeding and be successful."

Making personal decisions

Choices about sex, alcohol and labor pain relief are made within each woman's personal and cultural context. Kelly, Wilson and others say they hope their research has added valuable information that will enable women to make the best informed decisions during pregnancy.

Moore-Davis says that women should be asking their healthcare providers a series of questions about choices during pregnancy: "Can you tell me what the risk of that is? What are the benefits? What evidence supports your decisions in practice?"

And Kelly notes that a medically paternalistic view of pregnancy still exists that relies heavily on the precautionary principle, or the 'when in doubt, leave it out' approach. But, she says, "women are capable of making informed decisions based on the available evidence — it's fairly insulting to assume they cannot."